Furnace for producing physical and chemical changes in granular materials



Patented Mar. 31, 1953 FURNACE FR PRODUCING PHYSICAL AND CHEMICAL CHANGES IN GRANULAR MA- TERIALS Herbert A. Stein, Tempe, Ariz.

Application June 1, 1950, Serial No. 165,452

Claims.

This invention relates to method and means for heating solid granular materials which are light or fine, or both, to such a temperature as to drive off contained or combined moisture, or to eiect any desired physical or chemical change in said material. More specically, this invention relates to method and means for heating such materials in such a way as to subject said material to gradually increasing temperatures prior to surrounding each parti-cle with hot gases or flame so as to bring its temperature rapidly up to the maximum desired temperature.

Prior art methods of heating solid granular materials include passing them in a bed through a rotating tubular furnance which is heated at the discharge end, so that the waste gases from the final elevation of the material to its hottest temperature pass over the cooler material about to enter the hottest zone,` thereby providing gradual heating of the material and affording good fuel e'iciency. In this method, ner particles often fail to attain the degree of heat or treatment desired because agitation due to the rotation of the tube throws them into the stream of exhaust gases near the feed end, in which they leave the furnace without ever reaching the hot zone, or because the nner particles are shielded from the heat by a layer of coarser particles. One prior method which circumvents this failing of the conventional rotary furnace or kiln involves dropping the granular material into a flame passing through a tube or tunnel set at any angle, which carries the material out of the furnace. This method does not give suilicient retention time to render full treatment to the larger particles, and fails to provide gradual heating of the material up to the maximum temperature, which is required in many heating processes.

The purpose of this invention is to provide means for bringing granular solid material containing particles of different sizes up to any desired temperature, rst gradually up to some temperature below the maximum temperature desired, without affording an opportunity for the ner particles to leave the gradual heating zone and pass out of the furnace before passing through the high temperature zone. y

A further purpose of this invention is to provide means for throwing this gradually heated material into the flame or hot gases in the zone of maximum temperature in such a manner as to give each particle a retention time in the hot zone substantially proportional to itssize so that those larger particles which require more 2 time in the hot zone to attain the desired temperature or degree of treatment will be retained there longer, whereas the ilner particles will be held in the hot zone only ior a short time, thereby aording almost equal treatment to particles of different sizes.

Still another purpose of this invention is to provided means whereby the exhaust gases from the hot zone may heat a body of heat resistant material from which heat may pass by means of condition and radiation to the material entering the furnace in the gradual heating zone.

A more specific purpose is to provide a means for gradual heating to some intermediate temperature and iinal heating at a maximum temperature of such materials which require such treatment for expansion of their volume and consequent reduction in bulk density and grain density to form lightweight insulating aggregates and iillers, such as perlite and other expandable volcanic glasses, vermiculite, lclay pellets, and shales. In this application, the invention overcomes the difficulties encountered in prior art methods, such as the tendency for the product to be too light and friable because of too sudden heating to the final temperature required for expansion, and the tendency for coarser particles to be insufiiciently treated and expanded, which produces an aggregate of excessive density and inadequate insulating properties while using up more raw material per unit volume of finished product.

Other features of this invention will be set forth in the following specification and the drawing in which briefly:

Fig. 1 represents a section of the expansion furnace taken along a plane passing through the axis of the furnace tubes;

Fig. 2 is a detail view of the heat resistant strap suspension employed for the concentric furnace tubes;

Fig. 3 is a view of the front of the furnace tubes, and Fig. 4 is a view of the furnace tubes taken along the line li-t of Fig. 1.

The furnace of this invention -consists of three concentric tubes l, 2 and 3. The outer tube .I is provided with riding rings 4 which roll on trunnion rolls 5, one of which is powered by means of a variable speed motor B reduced by gears to a suitable speed. One set of trunnion rolls is provided with a means such as rims l for keeping the riding ring rolling on it from moving axially and falling oli the roll. The outer tube may be made'of mild steel but the inner -two tubes' -2 and 3 should be made of some heat resistant alloy.

The intermediate tube 2 is fitted at one end with a. scoop 3 which rotates with the entire assembly to pick up the raw material continuously fed into a trough 9 and lift the raw material into the space Iii between tubes 2 and 3. This space is the gradual heating zone, and is heated by conduction and radiation from the outside of inner tube 3 which is heated by contact with hot gases from the flames I I in the hot zone I2. The raw material is moved along the gradual heating zone Id towards the hot zone I2 by means of spiral nights I3. The inner tube 3 ends at a point somewhat short of the end of the intermediate tube 2, so that the main part of the hot zone I2 is bounded only by the walls of the intermediate tube 2.

These walls are provided with means for lifting the raw material which has now been heated in a gradual heating zone I0. This means consists of lifting flights I4 which are arranged in a spiral form so as to lift the heated material and drop it into the flame II in a multiplicity of sheets disposed at an acute angle to theflames II. At the same time the material is pushed slightly toward the source of the names II.

That portion of the heated material which is of small particle diameter is immediately brought up to the nal temperature and carried out of the hot YZone I2 through the inside of the tube 3 by the exhaust gases from the flames. Those particles which, being larger in diameter and requiring a longer time for the heat to penetrate into their interiors, are kept in the hot Zone for a proportionately longer time, since the ability of heat to penetrate into a particle and the ability of the exhaust gases from the flames to transport a particle are both directly proportional to the surface area of the particle per given mass, known also as the specic surface of the particle. As soon as a particle is expanded, in cases Where this invention is used in the manufacture of lightweight aggregates, the surface area per given mass is increased to the point where .the particle is readily carried out of the hot zione .in the jhot gases.

AIn the event that the raw material of the operation contains particles which are unexpandable due either to excessive size or being of unexpandable composition, pushed toward the name and finally .dropped into the space between the outer tube I and the in` termediate tube 2, where spirals i5, arranged in the opposite hand from that of spirals I3, move 2 towards the burners II and into the space bei tween the louter tube I and the intermediate tube 2. These are moved forward by the hot gases each time Vthey are lifted up and dropped into said gases by the lifters i4, and nally are deposited on the inner surface of the inner tube 3. In order to keep this material constantly resuspended in the hot gases which give the material its motion in a direction away from the hot zone, lifting vflights IG are provided in the these particles are 4 inner tube 3 to pick up the material which is dropped by the hot gases.

At the end of the furnace remote from the burners II, an end breeching I'I is provided to receive the material which is carried towards that end in the inner tube 3 and in the space between the outer tube I and the intermediate tube 2. This end breeching I'I also transmits the hot gases from the inner tube 3' into a pipe I8 which carries them to a dust collecting system which separates the nner components of the product from the hot gases. This material is ,eventually reunited with the materia1 which drops out of the breeching I1 through the chutes IS.

Since the flame is in most intimate contact with the inner tube or liner 3, and the outer tube or liner I vis exposed to the atmosphere, it is apparent that the inner liner 3 will expand most and the intermediate tube or liner 2 will expand less, while the outer liner I will expand least of the three. The expansion of the outer liner is taken up by a means which is conventional to rotary furnace construction, namely to allow one of the riding rings to run on a nat trunnion roll, thereby allowing the furnace shell to expand and contact with changes in temperature.

An important feature of this invention ccncerns the manner in which the intermediate tube 2 is attached to the outer` tube I so as to be always concentric with it yet allow for relative longitudinal and radial expansion. Fig. 2 is a detail View showing theform of suspension used for this purpose. The same method is used in suspending the inner tube 3 inside the intermediate tube 2. A piece of`heat resistant strap 20 .whose Vlength ,is substantially greater than the desired space between the concentric tubes .is bent in the shape of an S and attached firmly tothe two tubes in such an orientation that the direction of .relative movement betweenthe tubes or liners dueto expansion, indicated by arrows in Fig. 2, coincides with the direction in which the tails 2| Vof the S-shaped strap 2i] are pointed, These `straps 20 are indicated by the same number l20, in Fig.ll, a multiplicity of such straps being used around the circumference at each end of the inner liner and the intermediate liner. At any position of rotation of the furnace there are at least tWo such straps 2li in the position so that their .width is vertical and they are therefore rigidly supporting the inner tube concentric with the .next tube. It is to be emphasized that these straps do not .act as springs but rather as rigid supports capable of taking up dilerences in length and radius of .the supported tubes due to temperature changes.

Furthermore, a plurality of short arcuate vanes ida each having a width equal substantially to the width of the spacing between the tubes 2 and 3 are supported on the inside of the tube 2 in spaced and staggered'fashion for the purpose of protecting the straps 20 adjacent thereto, from the flames I I of the burner.

vIn addition to the-lifters i6, positioned on the inside of the tube `3, there may be provided spiral ights in the left hand end of this tube 3 to supplement the actionof the lifters I6 in removing material from the inner tube 3 into the end chamber I?. -These `spiral flights (not shown) would consist "of 'a spiral strip or strips oriented in the same manner as the spiral l5 so as to urge the material toward. the end chamber I'I when the tubes I, kZand 3 are rotated as des scribed. Furthermore, these spiral ights may extend throughout the length of the inner tube 3 or they may be only positioned in the left hand portion thereof and they may be positioned between the lifters I6.

The above disclosure of the details of this invention represents one of many possible embodiments, and it is not desired to limit this invention to furnaces constructed exactly as described, but rather it is desired that the appended claims be the measure of this invention.

What I claim is:

1. A furnace for producing physical and chemical changes in granular materials through heating, comprising two spaced concentric tubes, one of said tubes being inside of the other, means for rotating said tubes, a scoop attached to and rotating with said tubes for feeding granular raw material into the space between the said tubes as said tubes are rotated, heating means for heating one end of said tubes, said heating means comprising gas burner means for producing a gas flame extending well into the inner one of said tubes, and a wall for supporting said gas burner means on the furnace, spiral screw flights positioned in the space between said tubes for moving the raw material to the heated end of said tubes to heat said material, the inner one of said tubes being shorter than the outer one of said tubes, lifting nights attached to the inner surface of said outer one of said tubes adjacent to the flame end of the inner one of said tubes for lifting the heated raw material and for dropping it into the ame of said heating means for further heating to the necessary temperature to produce the desired physical and chemical changes in said material, means for drawing the hot gases produced by said flame through said inner tube, said gases carrying the finer and lighter components of the heated material through said inner tube, lifting flights to resuspend in the gases any part of said material that settles inside of said inner tube, an end chamber to receive the hot exhaust gases and part of said material carried thereby, and a dust collector for receiving the hot exhaust gases from said end chamber to separate the remaining part of said material from said gases.

2. A furnace for producing physical and chemical changes in granular materials through heating, comprising two spaced concentric tubes, one of said tubes being inside of the other, means for rotating said tubes, a scoop attached to and rotating with said tubes for feeding granular raw material into the space between the said tubes as said tubes are rotated, heating means for heating one end of said tubes, said heating means com prising gas burner means for producing a gas flame extending well into the inner one of said tubes, and a wall for supporting said gas burner means on the furnace, spiral screw flights positioned in the space between said tubes for moving the raw material to the heated end of said tubes to heat said material, the inner one of said tubes being shorter than the outer one of said tubes, lifting flights attached to the inner surface of said outer one of said tubes adjacent to the iiame end of the inner one of said tubes for lifting the heated raw material and for dropping it into the flame of said heating means for further heating to the necessary temperature to produce the desired physical and chemical changes in said material, means for drawing the hot gases produced by said ame through said inner tube, said gases carrying the finer and lighter components of the heated material through said inner tube, lifting flights to resuspend in the gases any part of said material that settles inside of said inner tube, an end chamber to receive the hot exhaust gases and part of said material carried thereby, and a third tube outside of the aforementioned two concentric tubes to shield said means for rotating said tubes from the heat transmitted through said two concentric tubes.

3. A furnace as set forth in claim 2 further comprising means between said third tube and said second tube for moving material rejected from the heated end of the furnace toward the other end of the furnace to be ejected therefrom.

4. ln a furnace for producing lightweight aggregates from expandable materials including volcanic glasses, perlite, vermiculite, clay, and shale, two concentric tubes, means for rotating said tubes, a scoop attached to and rotating with said tubes for feeding granular raw material into the space between the said tubes as said tubes are rotated, a spiral screw flight for moving the raw material from the feed ends to the opposite ends of said tubes, heating means positioned at said last mentioned ends of said tubes, said heating means comprising gas burner means for producing a gas flame extending well into the inner one of said tubes, and a wall for supporting said gas burner means on the furnace, said expandable raw material being exposed to the heat transferred from the hot inner tube to the space between said concentric tubes as said material is moved by said spiral screw flight, the inner one of said tubes being shorter than the outer one of said tubes, lifting nights attached to the inner surface of said outer one of said tubes adjacent to the flame end of the inner one of said tubes for lifting the heated raw material and dropping it into the flame of said heating means for further heating to the necessary temperature to expand it through the pressure of liberated gases insidethe softened mass, means for producing a reduced pressure to draw the hot gases produced by said flame through said inner tube, said gases carrying the expanded portion of the raw material through said inner tube, an end chamber to receive the hot gases and expanded material carried thereby, and a dust collector for separating the expanded material out of said gases.

5. A furnace for producing lightweight aggregates from expandable materials including volcanic glasses, perlite, vermiculite, clay, and shale, as set forth in claim 4 further comprising a third tube outside of said two concentric tubes for shielding said means for rotating said tubes from h heat transmitted through said concentric u es.

HERBERT A. STEIN.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 582,353 Hetherington May l, 1897 977,244 Wiebe Nov. 29, 1910 2,049,734 Fasting Aug. 4, 1935 2,165,128 Cheesman July 4, 1939 2,501,962 Pierce Mar. 28, 1950 2,521,190 Stafford et al Sept. 5, 1950i 

